This invention relates generally to automatic typewriters and, more particularly, to a combined forward and reverse indexing mechanism for use in such automatic typewriters.
Automatic typewriters are used in automated typing, computer, message transfer and other systems and applications. In such systems, these typewriters perform a data input and transmitting function and a signal receiving and data output function. During the first function, an operator strikes the typewriter keys simultaneously to type on that typewriter and, by means of various sensors, to transfer to signal processing equipment signals representing the typing operations being performed. In an automated typing system, this equipment comprises circuits for transferring the signals to a storage medium; in a computer system, a computer or an input/output controller; and in a message transfer system, another automatic typewriter.
During the signal receiving and data output function, the signal processing equipment transfers character and timing signals to the automatic typewriter. Various actuators cause the typewriter to print in response to these received signals.
A number of such automatic typewriters have been and are now available. They have become more popular, with the advent of code responsive, bail operated, electric typewriters. Such typewriters are marketed by IBM under the trademark "Selectric." These electric typewriters are sold both to offices for use as conventional electric typewriters and to other manufacturers for use as automatic typewriters in the foregoing and other applications.
Some automatic typewriters include a reverse indexing mechanism as well as a conventional, forward indexing mechanism. The inclusion of both mechanisms facilitates typing superscripts and subscripts and data plotting. As is well known, a forward indexing operation rotates the platen to a successive writing line on the paper, but does not return the carrier to the left margin, as a carriage return operation does. A reverse indexing mechanism rotates the platen "backward" to a new writing line above the original line on the paper.
There are several forward and reverse indexing mechanisms available in both standard and automatic typewriters. In some typewriters, separate forward and reverse indexing mechanisms even include separate power cams. This adds to the complexity and cost of the typewriter mechanism.
It has also been proposed to use a complex mechanical linkage to a single power cam effect both operations. An electromagnet is used to shift a pivot point for the linkage in response to signals from the signal processing equipment. This linkage, with its movable pivot, further complicates the typewriter mechanism.
Therefore, it is an object of this invention to provide a simplified forward and reverse indexing mechanism for use in automatic typewriters. Another object of this invention is to provide a reliable forward and reverse indexing mechanism for use in automatic typewriter.